(a) Field of the Invention
The present invention relates to a liquid crystal display device and, more particularly, to a liquid crystal display device in which printed circuit board (PCB) modules are suitably arranged to form a large screen with a high resolution.
(b) Description of the Related Art
In general, the liquid crystal display device includes a liquid crystal display module composed of a liquid crystal panel having a plurality of liquid crystal cells arranged in a matrix form between two glass substrates, and a back light unit disposed on the backside of the liquid crystal panel opposite to the display side; a PCB module disposed on the backside of the back light unit opposite to the display side; and a case for protecting and integrating those modules. Particularly, the PCB module is a driving circuit for processing externally applied red (R), green (G) and blue (B) video data and sync signals to supply video data, scanning signals and timing control signals to the liquid crystal panel, so as to allow the liquid crystal panel to successfully display application images such as computer images, television (TV) images, etc. The PCB module comprises a plurality of PCB's, and a plurality of flexible printed cables (FPC's) for signal transmission between the PCB's.
As is apparent from the schematic circuit diagram of a conventional liquid crystal display device as shown in FIG. 1, the PCB module, which is disposed on the backside of the display of the liquid crystal panel 50 to drive the liquid crystal panel 50 and has a relatively low resolution in the order of SVGA (600*800), comprises a main PCB 10 for processing externally applied RGB video data and sync signals by means of a timing-controller (T-con) which is a custom integrated circuit (IC) in the form of a flat pin grid array (FPGA), to generate video data and various control signals suitable to the structure of the liquid crystal panel; a gate driver PCB 20 equipped with a gate driver IC tape automated bond (TAB) for supplying a scanning signal based on the gate driver control signal received from the main PCB 10; and source driver PCB's 30 and 40 equipped with a source driver IC TAB for supplying video data based on the video data processed from the main PCB 10 and the control signals. The FPC, which is flexible cable for connecting the PCB's for signal transmission, includes an FPC that is to transmit various gate driver control signals 60 and 61 generated from the main PCB 10 to the gate driver PCB 20; a second FPC that is to transmit various source driver control signals 70 and 71 generated from the main PCB 10 to the source driver PCB's 30 and 40; and a third FPC that is to interconnect at least two main PCB's 10 which are separated from each other.
However, as the display device has a larger screen with higher resolutions such as XGA (768*1024), SXGA (1024*1280) and UXGA (1200*1600), some problems occur in regard to the width of data lines provided on the lower plate of the liquid crystal panel 50, the space for installing the source driver PCB's 70 and 71 and the driver IC TAB's provided on the lower plate of the liquid crystal panel 50, a rise of the data processing rate that requires a separate drive, etc. As such, the mostly used liquid crystal display device is of a dual bank type, which uses two separate source driver PCB's 70 and 71 that are respectively provided on the upper and lower part of the backside of the liquid crystal panel 50 to supply video data to the upper and lower parts of the liquid crystal panel 50.
FIG. 2 shows a PCB module of the conventional dual bank type liquid crystal display device for a large screen with a high resolution.
The dual bank type liquid crystal display device as shown in FIG. 2 has a liquid crystal display module 100; source drivers 110 and 120 provided on the backside of the display and connected to the upper and lower parts of the display by a main PCB 140 and FPC's 150 and 170; and a gate driver PCB 130 laterally connected to the main PCB 140 via FPC 160. The main PCB 140 has a timing controller for processing video data received via an external video data input signal line 180, and for supplying various data and control signals to the source driver 110 and 120 and the gate driver 130 via the FPC's 150, 160 and 170.
The above-described dual bank type PCB module as shown in FIG. 2 processes video data to form a large screen with high resolution in a bipartite drive manner, as follows. First, the main PCB 140 has a timing controller for processing video data from the external video data input signal line 180 to generate video data and various control signals, and sending them to the corresponding source driver PCB's 110 and 120. Here, the video data, i.e., R2n-1, B2n-1 and G2n are sent to the source driver PCB 110 on the upper side of the display via the FPC 150, and the video data, i.e., G2n-1, R2n and B2n are sent to the source driver PCB 120 on the lower side of the display via the FPC 170, so that the video data are displayed on the pixels of the liquid crystal panel in the order as shown in FIG. 3 as viewed from the front side of the display of the liquid crystal panel. Besides, the signals sent via the FPC's 150 and 170 include various control signal to be supplied to the source driver IC TAB as well as video data.
However, such a method in which various control signals in addition to video data are sent via the FPC's 150 and 170 to drive the liquid crystal panel on a large screen with high resolution incurs many problems in regard to coupling between signals more deviating from a tolerance range at an increased frequency, noises, and electromagnetic interference (EMI). Besides, when connecting PCB's with FPC's 150 and 170, the resistance capacitance (RC) intrinsic delay component caused by the coupling resistance between the PCB and FPC connectors and the other parasitic capacitance component results in both signal delay and signal distortion. Hence, an inadequate timing control between signals supplied to the source driver PCB's 110 and 120 provided on the upper and lower parts of the liquid crystal display module 100 makes setting and holding of video data inadequate to display. This causes noises or line defect on the liquid crystal display and, for the worse, provides a display that cannot be recognized. In particular, this problem becomes worse due to the longer FPC 170 shown in FIG. 2 rather than the shorter FPC 150.